Malt used for beer brewing is an ingredient which has strong influence over the determination of the taste or flavor of beer, and it is also said to be the most important thing of beer. Malt contains various components such as protein, starch, extract and the like, and the composition of said components sometimes determines the quality of malt. However, it is said that the quality of fermentation of wort made from said malt is the most important factor which determines the quality of malt. Beer is generally produced by grinding malt, mashing, filtration and boiling to prepare wort, followed by adding yeast to the cooled wort to proceed fermentation. Therefore, if the quality of malt is good, the fermentation of yeast will proceed actively, and beer wherein the flavor is also excellent can be produced. However, if the quality of malt is not good, the fermentation will proceed only very slowly, and it is possible that beer with little commercial value is produced.
Moreover, in beer brewing, fermentation is proceeded in a condition wherein the wort in which yeast is suspended, is left at rest in a fermentation tank. However, the following ability is required for the yeast: to ferment in a condition wherein the yeast is diffused into wort, to precipitate when the fermentation is completed, and to ensure the amount of yeast necessary for the next fermentation. As for lager type beer, bottom fermentation yeast is generally used, and most of these yeasts have the ability to flocculate between yeasts. The flocculation of the bottom fermentation yeast is an extremely valuable characteristic for the brewer. That is a characteristic wherein the bottom fermentation yeast is dispersed by sugar in the wort, to make a block by flocculating each other when sugar disappears after fermentation, then to precipitate and to separate from the liquid. However, malt also comprises materials that promote flocculation of yeast, and depending on the crop situation of barley of that year, there is malt comprising many materials that promote flocculation of yeast and it sometimes happens that yeast in the wort is precipitated at an early stage of the fermentation. Said materials that promote flocculation, are generally called premature yeast flocculation factors, and it is important to know how many premature yeast flocculation factors are comprised in the malt, when managing fermentation.
Therefore, it is very important to know the quality of malt, especially the characteristics of fermentation, before using malt in beer brewing. Recently, by chemical analysis, it became possible to know the content of protein, starch, extract and the like, and to estimate on some level when the the yeast is fermented. However, in order to know how much extract will be converted to alcohol when fermentation is actually proceed, or how much the premature yeast flocculation factor will precipitate yeast, it is necessary to actually prepare wort from malt, and to proceed fermentation. Therefore, the present inventors have reported a method of mashing malt or a method of fermentation test of a small scale to evaluate the quality of malt, especially the characteristics of fermentation, on a laboratory scale before the actual brewing, as a method of a fermentation test for evaluating malt (EUROPEAN BREWERY CONVENTION MONOGRAPH XXIII E.B.C.-SYMPOSIUM MALTING TECHNOLOGY ANDERNACH• GERMANY NOVEMBER 1994, 110-136). This method of fermentation test for evaluating malt has been established as a standard analysis, after many researchers have considered various aspects such as method of selecting malt used as control (called control malt), determination of control for mashing temperature, method of handling yeast and the like. By incorporating the results of chemical and physical analysis and the like to the results of this fermentation test for evaluating malt, a comprehensive decision is made, and the results are used as criterion when purchasing malt from a manufacturer.
The summary of the above-mentioned fermentation test for evaluating malt is explained in detail as follows: first, as for the process of grinding malt, the grinding scale of the disk mill is adjusted so that the intervals between disks are precisely 1.00 mm, 300 g of malt is ground with the disk mill, and the total amount is put in a 2 L mashing beaker (stainless-steel beaker). 1.8 L of tap water of 46 to 47° C. is added to the mashing beaker comprising the ground malt, the mixture is put into a large mash tun which the water temperature is adjusted to 45° C., and by continuing to stir, the mixture is mashed at a course of temperature according to the Congress method (45° C., 30 minutes→ raise temperature 1° C. every minute→70° C., 1 hour). When mashing is completed, the mash is filtered with a conical filtration cloth, and the filtration speed is determined. The amount of the wort which filtration is completed and the plato (° P.) are determined. 1.2 L of said wort is put in a 2 L conical flask, 2.6 g of fresh hop is added, the opening of the conical flask is covered with a funnel, and by boiling the mixture for 1 hour, the bubbling of the surface is examined. After boiling, the condition of Bruch and the clarity are examined. The boiled wort is cooled to around 50° C., filtered with Toyo filter paper No.2 (diameter 30 cm), then the filtrate is left overnight at around 8° C., filtered with Toyo filter paper No.2 to remove cold breaks, and then tap water is added to adjust the plato of wort to 11.0° P. The wort obtained which has been boiled is used in the fermentation test.
Approximately 500 ml of yeast in a form of mud collected from the fermentation tunk is put in a 1 L beaker, an equal amount of cold water is added, stirred well, and when the yeast is precipitated, the supernatant is thrown away. This operation is repeated for 4 times or more, and the liquid is filtered with a 100 mesh wire net. By using a Buechner funnel with a Toyo filter paper No.7 attached to it, yeast suspended solution is filtered by aspiration to obtain pressed yeast. 500 ml of said wort which has been boiled, and 1.75 g of pressed yeast are added to a 1 L flask for fermentation test, the mixture is shaken 30 times to disperse the yeast, and is left at rest for 2 hours at a constant temperature (20° C.±1° C.). Yeast-added wort thus obtained is moved to a KI fermentation tube (capacity of 500 ml, diameter 25 mm, height 1250 mm) and is left at rest at 8° C.±0.2° C. for 7 days. As control, control malt is used. OD 800, plato, AAL (apparent attenuation limit), and premature flocculating nature of yeast are determined for 1 to 8 days, compared with the control, and the fermentation characteristics of the test malt are evaluated.
The above-mentioned fermentation test for evaluating malt is an excellent method that has been established as a standard analysis to evaluate the fermentation characteristics of malt. However, during the process of considering the method in order to obtain more reproducible test results, it was found that the physiological condition of yeast to be used could possibly be a factor having influence over the test results. That is, the fermentation test for evaluating malt is a kind of bioassay by a yeast. Generally, yeast collected after actually being used in a beer plant (plant yeast) is used in the above fermentation test for evaluating malt, but in a beer plant, as there are busy season, off season or manufacture discontinuation due to maintenance and repairing, not only it is hard to collect yeast in the same physiological condition at all times, but also the fermentation activity of the yeast may change depending on the storage condition or transportation condition of the yeast. Moreover, in case a malt manufacturer conduct independently a fermentation test for evaluating malt or a beer manufacturer outsource a fermentation test for evaluating malt and the like, it is not always possible to use yeast collected from a beer plant in the same condition. Thus, it was estimated that there were problems for the reproducibility of the test results. The object of the present invention is to provide a method of preparing yeast usable in a fermentation test for evaluating malt on a laboratory scale, in order to obtain more reproducible test results, without being influenced by the operating conditions of the plant or the like, and a medium to be used therein.